1. Field of the Invention
This invention relates to the production of dehydrocoupled toluene products. It is particularly related to the oxidative synthesis of 1,2-diphenylethylene (stilbene) from toluene and to inorganic metal/oxygen compositions effective for oxidatively coupling toluene to produce stilbene.
Stilbene, because of its unsaturated character is very reactive and may be employed in various organic syntheses. Derivatives of stilbene are useful in the production of products which may be used in the manufacture of dyes, paints and resins. It is also useful in optical brighteners, in pharmaceuticals, and as an organic intermediate.
2. Description of the Prior Art
Dehydrocoupling of toluene by the reaction with lead oxide to form stilbene has been reported by Behr and Van Dorp, Chem. Ber., 6, 753 (1873) and Lorenz, Chem. Ber., 7, 1996 (1874). In this reported work, stilbene is obtained by conveying toluene over lead oxide maintained at or about at a dark red glow. The coupling of toluene using elemental sulfur as the coupling agent has been reported by Renard, Bull. Soc. Chim. France, 3, 958 (1889); 5, 278 (1891) and the types of products produced by such coupling reactions have been discussed by Horton, J. Org. Chem., 14, 761 (1949). More recently, U.S. Pat. No. 3,476,747 discloses arsenic pentoxide, antimony tetroxide, antimony pentoxide, bismuth trioxide, and manganese arsenate as oxidants for the oxidative dehydrocoupling of toluene to form 1,2-bis(aryl)ethylenes. Similarly, U.S. Pat. No. 3,494,956 discloses lead oxide, cadmium oxide, and thallium oxide as suitable oxidants, and in Example 9 a mixture of toluene and oxygen passed over heated lead oxide produced bibenzyl. In U.S. Pat. No. 3,557,235 the stoichiometric toluene coupling reaction is taught using an oxide of bismuth, lead, tellurium, barium, thallium, cadmium, or mixtures thereof which serves as the source of oxygen in the reaction. U.S. Pat. No. 3,963,793 teaches the use of bismuth trioxide and thallium trioxide or mixtures thereof supported on basic carrier materials selected from the oxides of Group 2a elements and having a minimum surface area of 20 m.sup.2 /g as suitable for toluene coupling to produce bibenzyl. The addition to the supported catalyst of small amounts of silver as a promoter is also disclosed. In U.S. Pat. No. 3,965,206 oxides of lead, cadmium, bismuth, and mixtures thereof are taught as suitable oxidants for toluene coupling. This patent also teaches the disproportionation of the stilbene with ethylene to produce styrene. U.S. Pat. No. 3,980,580 discloses an oxygen composition of lead, magnesium, and aluminum as an oxidant for toluene coupling. Also, U.S. Pat. No. 4,091,044 discloses oxygen compositions of lead and antimony and optionally with bismuth as oxidants for toluene coupling to form stilbene.